1. Field of the Invention
The present invention relates to a method and apparatus for resetting a MAC-ehs protocol entity of a wireless communications system, and more particularly to a method and apparatus for improving reset of a MAC-ehs protocol entity for a user equipment in a wireless communications system, so as to enhance system efficiency.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS (Quality of Service) requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate.
HSDPA and HSUPA adopt Hybrid Automatic Repeat Request (HARQ) technology to enhance retransmission rate and reduce transmission delay. HARQ is a technology combining Feed-forward Error Correction (FEC) and ARQ methods, which makes a Universal Terrestrial Radio Access Network (UTRAN) trigger retransmission according to positive/negative acknowledgement signals (ACK/NACK) transmitted from a user equipment (UE), and the UE stores useful information about the last failed transmission for later use.
To further increase transmission efficiency, 3GPP newly introduces an evolved high speed Media Access Control (MAC-ehs) protocol entity in the MAC layer to support segmentation, reordering, and reassembly of Radio Link Control (RLC) Protocol Data Units (PDUs) with variable lengths. In addition, the MAC-ehs protocol entity can further multiplex data of various priority queues to a MAC-ehs PDU in a Transmission Time Interval (TTI) for enhancing the flexibility of data scheduling.
Besides, in order to advance a reordering functionality of the MAC-ehs protocol entity, the 3GPP further introduces a reset timer for each priority queue, which is mainly used for resetting a receiver window of the reordering functionality when no PDU is successfully received by the UE for a specific duration, i.e. an expiry time of the reset timer, for avoiding following received PDUs being discarded incorrectly. Detailed operations of the MAC-ehs entity and the reset timer can be found in the MAC protocol specification formulated by the 3GPP, and are not narrated herein.
Accordingly, the prior art provides a first reset function and a second reset function in the MAC-ehs protocol entity to respectively satisfy reset requirements of the upper layers and the reset timer. The first reset function is performed by request of upper layers, such as a Radio Resource Control (RRC) layer, for resetting the MAC-ehs protocol entity when configurations of the UE are changed, e.g. during handover; the second reset function is activated when any reset timer in the MAC-ehs protocol entity expires for resetting the reordering functionality of the MAC-ehs protocol entity. When either of the first reset function and the second reset function is performed, all configured HARQ processes are flushed.
However, according to the above MAC protocol specification, when the first reset function is performed by the request of the upper layer, the reset timer is not stopped. Thus, it is very likely that the second reset function will be activated in a short period of time due to expiration of the reset timer, and steps like flushing all configured HARQ processes will be repeated. In such a situation, data stored in the HARQ buffer that has not been successfully decoded during the time the first reset function and the second reset function are successively activated is all discarded, so as to decrease the probability of successful decoding by the UE.
In short, since the second reset function may be activated incorrectly in the prior art, the probability of successful decoding by the UE is decreased.